Power is generated in a compression-ignition diesel engine such as a diesel engine by diffusing and combusting diesel fuel or alternate liquid fuels in a plurality of engine cylinders. Liquid fuel is injected into the engine cylinders that are full of compressed air at high temperature. The fuel is broken up into droplets that evaporate and mix with the air in the cylinders to form a flammable mixture. Complete and efficient combustion in the cylinders requires full oxidation of the fuel though evaporation, species diffusion, and mixing with air, and timely heat release during the combustion process. Thus, the amount of cylinder-charged air, or air to fuel ratio of the mixture, plays an important role in diesel engine fuel-air mixing and combustion, which, in turn affects fuel efficiency, exhaust emissions and engine thermal and mechanical loadings. This is particularly true for quiescent chamber type medium speed heavy-duty diesel engines where the cylinder air intake swirling is slight, such as locomotive, marine or stationary power engines having cylinders with relatively large displacement volumes. The fuel injection timing of medium speed diesel engines burning diesel or alternative fuels and operating at full load is typically set so that the actual peak firing pressure in the cylinders is at or below a maximum allowable cylinder firing pressure for a given intake air temperature and pressure as determined by ambient conditions.
Engine exhaust emissions, including carbon monoxide (CO), particulate matters (PM) and smoke are generated when the air-fuel mixture is incompletely combusted. When engines are operated at higher ambient temperatures and higher altitudes, i.e., at a low barometric pressure, or at a higher ambient/engine inlet air temperature, or both, lesser amounts of air are introduced into the cylinders, causing the air-fuel mixing process to be deteriorated relative to lower intake air temperatures and lower altitude, higher ambient pressure and normal ambient/inlet air temperature environments. This combination of factors increases late and incomplete combustion in the engine cylinders which lowers fuel efficiency and increases exhaust emissions of CO, PM, and smoke. The reduced amount of air for the fuel-air mixture combustion, together with the increased late and incomplete combustion, typically leads to reduced peak cylinder firing pressure and increased cylinder exhaust gas temperatures. For engines including a turbocharger, the decreased barometric pressure or increased ambient/inlet air temperature or both resulting in the increased exhaust temperature causes an increase in turbocharger speed and thermal loads on cylinder exhaust and turbocharger components. This may require a reduction of power output to prevent turbocharger damage from overheating and excessive speed. Also as ambient/inlet air temperature becomes lower than normal, peak cylinder firing pressure increases thus increasing mechanical loading on engine cylinder assembly components and affecting the engine reliability and durability.
U.S. Pat. No. 6,158,416 describes a diesel engine control scheme for high altitudes wherein engine speed and fuel injection timing are adjusted in response to a sensed barometric pressure and engine throttle position. U.S. Pat No. 6,286,480 describes a diesel engine control scheme for high altitudes wherein fuel injection timing is adjusted in response to a sensed barometric pressure and engine throttle position. U.S. Pat. No. 6,325,050 describes a diesel engine control scheme wherein fuel injection timing is controlled in response to measured values of barometric pressure and manifold air temperature. Each of these three patents is incorporated by reference herein.